Anti-inflammatory agents have been used to treat fibrosis with the aim of suppressing chronic inflammation, but such treatments can be unsatisfactory in terms of efficacy and side effects. Numerous studies have been performed to obtain substances that inhibit the production or the activity of the cytokines thought to be involved in fibrosis. Tranilast (n-[3,4-dimethoxycinnamoyl] anthranilic acid; product name Rizaben™) is an anti-fibrotic agent used in Japan for the treatment of fibrotic skin disorders such as keloids and scleroderma. Although the precise mechanisms and mode of action of tranilast are incompletely understood, its ability to inhibit ERK phosphorylation, a major intermediate in the TGF-β signalling pathway, may underlie its antifibrotic effects, with known actions of tranilast including the inhibition of TGF-β-induced extracellular matrix production in a range of cell types. Tranilast has also been shown to attenuate TGF-β-induced collagen synthesis in cardiac fibroblasts using an experimental model of diabetic cardiac disease, and to reduce inflammation in allergic diseases, such as allergic rhinitis and bronchial asthma, etc. In addition, tranilast has been shown to have anti-proliferative activity.
However, it has recently been shown that genetic factors in certain patients may confer susceptibility to tranilast-induced hyperbilirubinemia. One possibility for how this may arise is the presence of Gilbert's syndrome polymorphisms of the glucuronosyltransferase UGT1A1, which leads to increased susceptibility to tranilast-induced hyperbilirubinemia. Such hyperbilirubinemia may result from the low level of UGT1A1 glucuronosyltransferase present in individuals with this syndrome. Tranilast itself, and its major metabolite N3 (4-desmethyl-tranilast), have been shown to be inhibitors of UGT1A1, potentially leading to aberrant metabolism of bilirubin and its accumulation.
Accordingly, compounds that are based on tranilast have the potential to provide compounds that may have pharmaceutical properties with potential anti-fibrotic, anti-inflammatory, and anti-proliferative or anti-neoplastic activity, and as alternatives/adjuncts to tranilast. These compounds may also have altered and/or improved metabolism relative to tranilast.